Mechanics class rocket

[dharak1]

So today I had the first day of grade 8 and found out that we need to make a rocket very soon because of the weather so I started designing my rocket and I need to know a few things and maybe some help on the design. I already have a rocket plane called the Wyvern and there are 3 of them each launch uses 2 C6-3 engines. It has amazing results for what you would expect out of strapping 2 medium level power rockets to a foam plane. I can post pictures if you want. This next one has 3 engines 2 C6-7 engines and 1 A1/2 with an undetermined fuse time (do rockets that small even use ejection charges? the smallest I have used is a . And it looks a LOT like an Ares V I think somewhere in my subconscious all of my rockets are inspired by Ares rockets. It has 6 fins 4 placed around the center as usual then 2 on the side of the C6-7 rockets opposite the center. Any problems seen here? The top is obviously pointed and all of the engines will be tightly fastened with 30 day stucko tape. The A1/2 is there for the chute only and if it doesn't have a charge I may have to go to a bigger engine. Names would also be appreciated.

[NGTOne]

Man, I wish my elementary school classes were half as cool as yours... post some pics of your designs!

[dharak1]

This is pretty much extra-curricular the only related part to school is the rockets I figured I may as well have some fun on my way.

Designs for the un-named rocket: http://i.imgur.com/yFp9bEeh.jpg

Wyvern Pi (picture is blurry): http://i.imgur.com/HhaIEqYh.jpg

Wyvern 3 (currently in the process of getting prepared to be a payload propeller plane): http://i.imgur.com/lArifZSh.jpg

Wyvern 2 (A moment of silence, Wyvern 2 collided with a power line while under powered flight): http://i.imgur.com/18xbUPxh.jpg

Wyvern 1 ( The second plane the first was Wyvern 0 that was a prototype based off of a partially broken plane): http://i.imgur.com/Nc6bE67h.jpg

Those are all the planes, Wyvern Pi was going to be Wyvern 4 but a collision with the ground caused a damaged wing that was moved to Wyvern Pi/4 because i figured it better to have 3 fully complete planes and 1 kind of damaged one, rather than 2 working and 2 damaged.

[Kerbart]

An important step in design is deciding what you want to achieve. Do you want to reach a certain height? Is keeping it straight the main challenge? Or does it just have to look good?

As for names, what you can do is google some kind of mythology. Be it Greek, Roman, Nordic, Celtic, Aztec, Papua... and then name your rockets after the appropriate gods of the sky. It will impress everyone when you can say "this one is called Pluvius, for the Roman god of the rain" or something along those lines.

[dharak1]

I want it to get above most model rocket kits (around 1.5 Km) AND look good. I hope it will steal the show especially after I send up Wyvern 1 My other designs were around 4 feet long and used 4 D12-7 engines and launched off of metal rods on three sides. The Wyvern also need to be revised because the launch system is just placing a rock under the front to angle it up.

[K^2]

Most C engines are gun powder-based. Estes motors in the A-E range certainly are. To break 1.5km even in ballistic regime you'd need over 170m/s of delta-V, and at that point drag is going to be significant. These kinds of motors will only give you about 30s of I_SP, so it'd be nearly impossible to break 1.5km.

If you are really planning to go that high, you need to go with composite motors. These can have I_SP well in excess of 200s. With one of these you can have effective delta-V nearing speed of sound, and that's going to be enough to give you 2-3km of altitude if drag isn't too heigh and you get your rocket to fly straight. The composites typically start roughly with the F class. These do cost 2-3 times more than regular motors, and they do require special igniters and launch system, but on the plus side, they aren't considered high power rockets, so you do not need special kind of licensing. All of the standard precautions apply.

This is something to work up to gradually, and maybe I'd start with the D and E rockets, maybe even something with an E booster and C primary stage to see how far you can get that. But if you are going fore altitude, composites are your goal.

[dharak1]

I was actually checking out G rockets because I can get one online for the test for level 1. I will check out higher level rockets too.

[K^2]

All rocket motors are a little different, but Estes G40 have about 1km/s of delta-V in them. You can probably expect something similar out of other G motors. Of course, that's without any payload whatsoever. Reasonably, you could expect about 400m/s out of your rocket. Again, most of that will be eaten up by drag, so in reality the rocket will never get even close to Mach 1, but it should still be enough to get a couple of kilometers of altitude out of it, at least. So yeah, a G motor should do it. It just needs a rocket with a nice, aerodynamic body and good stability.

Keep in mind that as you scale up the motor, you need to scale up everything else. The amount of clear space for launch, distance between you and the rocket when you launch it, and so on.

[dharak1]

Ok, a few things I overlooked that my grandfather saw.

1. this thing is going HIGH in the middle of a city too. It can't be launched with that much power when it can land in nearly any of 700000 peoples backyards. this means I'm going with 2 C6-7 engines and an A 1/2 like before.

It will still trump the competition, making it myself gets me another 20 points out of 250 counting bonus marks. It will go higher than the other 30 people launching A rockets and the 10 launching B rockets and the 3 launching low power C rockets.

2. Launch system. I have to remake the Wyvern launch system completely, it's an insult to call it a system we find the nearest broken asphalt or rock we can and lean it up. I hope to eventually make 1 system for all rockets that can tilt for planes and go vertical for rockets. For now 2 different systems for the rockets but the alligator clips on a 12 meter wire work pretty good still. Just put one to the back of the cigarette lighter and one to the side and watch er go. I will use dowels for rails and fasten them on wood boards for the launch. For the plane same thing but with a tilted launch at around 30 degrees.

That's all Have for now but since I am using smaller rockets I can get them here and do tests NOW!

[K^2]

NAR regulations recommend 1,000 feet clearance for any F motor launches. 400 feet for the C motors. So yes, if there is limited open space, definitely go smaller. Though, even with a pair of C motors your rocket might cover more ground if it goes off course and knock someone's window out. So be careful, and do the tests as far away from everything as possible to make sure your rocket flies true.

For launch system, take a look at commercial systems. They aren't expensive, if you want to just buy one, or if you are required or just want to build your own, they might give you some good ideas. All of them effectively consist of a metal rod that can be angled for plane launches, a metal plate at the bottom of the rod to act as the firewall, and a tripod holding all of this fixed on the ground.

For the electronic launch of multiple motors, what I found to work best is using commercial igniters wired in parallel and taking the wire to the car battery. Unlike the cheap AA battery launchers, the moment you touch wires to the car battery, the igniters will go off, so there is no guessing on when the rocket will take off, and you get as close to simultaneous ignition as possible.

That said, even with simultaneous ignition I've had trouble keeping a multi-motor rocket on a straight path. If you want something reliable, it's really best to have one motor per stage.

[dharak1]

The plane had to have two motors for balance but this one is for load. Because its constructed from reinforced pop cans i may fill one and slip it in to show the power of rockets. I don't think people in the class realize the power these things have. We went through a several page booklet today about how Apollo and other programs like Mercury made some of our tech today possible. A TON of people fell asleep I am the only one with any understanding of rockets. In today's class a girl talked about that Felix guy and when she explained it said "but he didn't go high enough to where you are floating in zero gravity" I could let the gravity and G slide but it was the fact that she didn't know that orbit was freefall. I know and understand she's a girl and most girls aren't interested in that stuff, most people in my school don't understand mass and weight or the way orbits and transfers work. I though it was common knowledge When I brought it up with my grandfather a few months ago he understood that all and he ended schooling and most information absorbing in 1971 before the end of Apollo. I'm not trying to be rude but it amazes me how little people care. Either way i am using low millimeter rocket bodies on the sides now so I can swap between A B C and D rockets. I hope to order them tomorrow so they get shipped ASAP.

Also for ignition i hook up igniters in parallel so there should be 0 delay nearly. I have tons of amps and volts to work with too.

Parts for Wyvern 3 came in today so I will have a prop plane to fly around the rockets too.

Edited September 7, 2013 by dharak1